A circuit breaker can protect against fires by breaking an electrical circuit in a building's power line in response to detecting a dangerous situation, such as an overload condition or a short circuit condition. Often, a homeowner or a technician can manually reset a switch in the circuit breaker when the dangerous situation has passed.
Another mechanism associated with a circuit breaker is an arc fault detector, which uses electronics to analyze the characteristics of waveforms exhibited in power signals when a device is plugged into a power line of a building. The arc fault detector determines whether electrical arcing is occurring in a device plugged into the building's power line. The arc fault detectors conclude, based on the power signal's characteristics, whether arcing is occurring. Generally, if the signal's waveform characteristics fall within a predetermined set of parameters, the arc fault detector determines that a dangerous condition exists and causes a circuit breaker to shut off electrical power to the power line, and thereby to the plugged device.
One type of arc fault detector is disclosed in U.S. Pat. No. 7,136,265 issued to Kon B. Wong. In this reference, a method and system is disclosed for determining whether arcing is present in an electrical circuit. The method includes sensing a change in an alternating current in the circuit and developing a corresponding input signal, analyzing the input signal to determine the presence of broadband noise in a predetermined range of frequencies, producing a corresponding output signal, and processing the input signal and the output signal in a predetermined fashion to determine whether an arcing fault is present in the circuit. The processing includes determining a type of load connected to the electrical circuit, based at least in part upon the input signal and the output signal, and monitoring high frequency noise in a 20 KHz band for each ⅛ cycle of the alternating current. Another type of arc fault detector is disclosed in U.S. Pat. No. 7,460,346 to Vijay V. Deshpande. Both of these references are incorporated by reference in their entirety.